Recently, there has been enormous interest in growth of Group III nitride, and particularly gallium nitride (GaN) thin films, Jpn. J. Appl. Phys. Vol. 34 (1995) pp. L 797-L 799. GaN, and related (Aluminum, Indium)N alloys are being utilized for the production of efficient optoelectronic devices, e.g. light emitters and detectors spanning the spectral range of visible to deep ultra-violet (UV). In addition, the direct wide bandgap and the chemical stability of Group III nitrides are very beneficial for high-temperature and high-power operated electronic devices, e.g. hetero-junction bipolar and field effect transistors. However, the poor material quality of GaN severely limits the efficiency of such devices.
When GaN is directly grown on a sapphire substrate, the growth mode is three-dimensional due to the large lattice mismatch, the chemical dissimilarity, and the thermal expansion difference. The layer contains structural defects such as point defects, misfit dislocations, and stacking faults. These defects degrade the film""s structural, morphological, and electronic properties. In order to achieve high quality epitaxial growth, researchers have introduced a thin low-temperature grown AlN or GaN layer serving as a buffer layer. This layer provides nucleation sites for subsequent two-dimensional GaN growth at higher temperatures, see H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki, Jpn. J. Appl. Phys. 28, L2112 (1989) and S. Nakamura, T. Mukai, M. Senoh, and N. Isawa, Jpn. J. Appl. Phys. 31, L139 (1992). Therefore, the control of buffer layer growth is the most important step in the improvement of GaN main layer properties. The effect of buffer layer thickness and growth temperature on GaN main layer properties has been well studied: G. S. Sudhir, Y. Peyrot, J. Krxc3xcger, Y. Kim, R. Klockenbrink, C. Kisielowski, M. D. Rubin and E. R. Weber, Mat. Res. Symp. Proc. 482, pp. 525-530 (1998); Y. Kim, R. Klockenbrink, C. Kisielowski, J. Krxc3xcger, D. Corlatan, Sudhir G. S., Y. Peyrot, Y. Cho, M. Rubin, and E. R. Weber, Mat. Res. Symp. Proc. 482, pp. 217-222 (1998); J. Krxc3xcger, Sudhir G. S., D. Corlatan, Y. Cho, Y. Kim, R. Klockenbrink, S. Rouvimov, Z. Liliental-Weber, C. Kisielowski, M. Rubin and E. R. Weber, Mat. Res. Symp. Proc. 482 pp. 447-452 (1998). Buffer layers for Group-III nitride growth has been discussed in Mohammad et al., xe2x80x9cProgress and Prospects of Group-III Nitride Semiconductorsxe2x80x9d, Prog. Quant. Electr. 1996, Vol. 20, No. 5/6 pp. 418-419, hereby incorporated by reference in its entirety. Various buffer materials are disclosed. Not disclosed or fairly suggested is gallium metal.
Group III nitride semiconductors are discussed generally in Mohammad et al., xe2x80x9cProgress and Prospects of Group-Ill Nitride Semiconductorsxe2x80x9d, Prog. Quant. Electr. 1996, Vol. 20, No. 5/6 pp. 361-525, the contents of which are hereby incorporated in its entirety.
Other U.S. Patents relevant to the state of the art include U.S. Pat. Nos. 5,369,289; 6,133,589; 5,767,581; 6,013,937; 5,578,839 and 5,290,393. U.S. Pat. No. 5,369,289 discloses a gallium nitride based compound semiconductor light emitting device comprising a buffer layer of a gallium nitride compound. U.S. Pat. No. 6,133,589 discloses an AlGaInN based light emitting diode having a buffer layer comprising a AlFaInN-based material. U.S. Pat. No. 5,767,581 discloses a gallium nitride based III-V group compound semiconductor having an ohmic electrode comprising a metallic material. U.S. Pat. No. 6,013,937 discloses a silicon wafer having a buffer layer formed on the dielectric layer. U.S. Pat. No. 5,578,839 discloses a gallium nitride based compound semiconductor device. U.S. Pat. No. 5,290,393 discloses a gallium nitride based compound semiconductor having a buffer layer of GaAlN. The above mentioned references and U.S. Patents are hereby incorporated into this specification in their entirety.
In this work, we propose a novel growth procedure to grow high quality epitaxial Group III metal nitrides, particulary GaN thin films on lattice-mismatched substrates. In contrast to all other prior art, we are using a pure metallic Group III metal layer serving as a buffer layer. The resulting main layer exhibits superior structural and electrical properties.
The present invention relates to a process for growing an epitaxial metal nitride on a substrate, and to the metal nitride wafers made by the process. More particularly, it relates to a process for growing an epitaxial metal nitride on a lattice mismatched substrate in which a buffer layer of a Group III metal is deposited on the lattice mismatched substrate, and a Group III metal nitride thin film is thereafter grown on top of the buffer layer. The invention also relates to metal nitride semiconductor wafers each of which is a composite comprising a substrate, a buffer layer of a metal overlying the surface of the substrate, and a top layer of an epitaxial metal nitride thin film.
The invention contemplates that any Group III metal is sufficient to accomplish the purpose of this invention. Preferred is an aluminum or gallium metal. Particularly preferred is gallium.